You want to know if you can stack loads of really high-powered weapons and turn them on and off in order to stop your whole ship shutting down, no?
You can, but you'll still need to switch something on to trigger them to switch off, and that module will need to be deactivated for the entire time you want to use the turrets.
Basically, put them on their own at the lowest priority that will keep them active with hardpoints deployed, but have a module (an SCB perhaps) switched off at a higher power priority than the turrets. When you switch on the SCB, the power demand will trip the power management systems and shut off the beam lasers.
Like I said, the drawback is that you have a module that is effectively useless most of the time and is only being used in very specific circumstances. Depending on the size of your ship, this might be a compromiise too far. Switching firegroups will be quicker.